Patent Document 1 below discloses a method of searching for the position of travel equipment by a PHS, which can accurately search for the position of travel equipment such as a truck, a pallet for loading, or the like, by accurately estimating tolerance and accurately estimating a loading time.
According to this searching method, a PHS terminal is mounted on the travel equipment, estimated distances between the PHS terminal and three or more neighboring base stations are calculated from the radio field intensities of signals from the base stations, a plurality of circles having the positions of the base stations as their centers and having the estimated distances as their radii, respectively, is obtained, and then the position of the travel equipment on which the PHS terminal is mounted is obtained from the crossing ranges of the circles.
Also, if the position of the travel equipment is within a predetermined tolerance from a predetermined strongpoint position, it is determined that the travel equipment is in the strongpoint position.
Patent Document 1: Japanese Patent Application, First Publication No. 2007-43343